1. Field of the Invention
The present invention is generally related to a liquid crystal display and a method of driving the liquid crystal display. More specifically, the present invention is related to an active matrix type liquid crystal display, and a driving method thereof.
2. Description of the Related Art
An active matrix liquid crystal display (AMLCD) is known in the technical field. The active matrix liquid crystal display has a plurality of pixels which are arranged in a matrix form. Active devices such as TFTs (Thin Film Transistor) are provided for respective of the plurality of pixels. A gate electrode of each active device is connected to a scanning line formed along a row direction, and a drain electrode of each active device is connected to a data line formed along a column direction. The liquid crystal display scans the scanning lines sequentially from top to bottom of a display panel, to display an image on the display panel (namely, line sequential method). Such an operation for displaying a single image is referred to as a “frame (field)”.
In the liquid crystal display within the public domain, a voltage is applied to the pixel through the data line. The voltage is referred to as a “pixel voltage” hereinafter. A polarity of the pixel voltage is inverted every predetermined period. Thus, the pixel is driven in an AC (Alternating Current) manner. Here, the polarity indicates whether the pixel voltage is positive or negative with regard to a voltage of a common electrode as a reference voltage. The above-mentioned driving method is applied in order to suppress the deterioration of a liquid crystal material. For instance, the polarity of the pixel voltage is inverted every time two scanning lines are scanned (2-line inversion driving method). That is to say, assuming now that a first scanning line is scanned after the polarity of the pixel voltage is inverted, the next scanning line (namely, a second scanning line) is scanned with the same polarity, and then the polarity is inverted again. Due to the 2-line inversion driving method, the flicker can be reduced and the image quality can be improved.
The increase in size of the liquid crystal display causes the increase in parasitic capacitance and parasitic resistance. As a result, a waveform of drive voltage applied to the data line is rounded. Also, as the resolution of the liquid crystal display panel becomes higher, the time during which the pixel voltage is applied to the pixel becomes shorter (the time is referred to as a “writing period” hereinafter). These facts may cause that in the 2-line inversion driving method, a voltage (holding voltage) which is written to a pixel connected to the first scanning line becomes lower than a voltage which is written to another pixel connected to the second scanning line. When the holding voltage of the pixel becomes lower, the luminance of the pixel also becomes lower. Thus, a difference in the luminance between adjacent scanning lines appears as a lateral stripe on a display screen. For suppressing the occurrence of such a lateral stripe, the following techniques have been proposed; Japanese Laid Open Patent Application No. 2001-215469 (referred to as patent document No. 1 hereinafter) and Japanese Laid Open Patent Application No. 2002-287701 (referred to as patent document No. 2 hereinafter).
According to liquid crystal displays disclosed in the patent document No. 1 and the patent document No. 2, the writing period T1 with respect to a pixel connected to a first scanning line is designed to be longer than the writing period T2 with respect to a pixel connected to a second scanning line. Therefore, the luminance of the pixel connected to the second scanning line can be suppressed nearly to the luminance of the pixel connected to the first scanning line. As a consequence, the occurrence of a lateral stripe on a display screen may be suppressed, although the contrast deteriorates.
Also, according to the liquid crystal display disclosed in the patent document No. 2, when the second scanning line is scanned, a precharge voltage which is intermediate between a voltage of a positive electrode and a voltage of a negative electrode is once applied to the pixel (precharging operation), and then a predetermined pixel voltage is applied to this pixel. As a result, the occurrence of the lateral stripe on the display screen may be suppressed. However, currents are consumed in the precharging operation, and thus the power consumption is increased.